ABSTRACT
The United Downs geothermal power project has been developed by Geothermal Engineering Ltd (GEL) and is the first geothermal electricity project in the UK. The site was selected in 2010 for its geology (strongly faulted, radiogenic granite), surface infrastructure, grid connection and potential community acceptance. The deep drilling programme started in 2018, with the production well drilled to 5,275 m MD and deviating from 3,390 m to a final inclination of 33.5º, representing the deepest onshore well in the UK. The injection well was then drilled to 2,393m MD, deviating from 1,020 m to a final inclination of 40º. The drilling of a deep production well and shallow injection well into a natural fault zone is a concept developed by GEL, based on some of the results from the research at the Hot Dry Rocks project in Rosemanowes, Cornwall. The production well has successfully encountered significant permeability horizons within the target fault zone, temperatures of 180ºC and world-class lithium concentrations. It is expected to provide between 2 and 3 MWe to the National Grid and carbon neutral heat to a proposed 6 km heat main and the project has been associated with many universities and pan European research projects. Despite the delays caused by the Covid-19 pandemic, the United Downs project has seen a number of exciting milestones since EGC 2019, including completion of drilling, extensive well testing/stimulation and signing of the first Power Purchase Agreement (PPA) for deep geothermal electricity in the UK with Ecotricity. The team also secured grant funding for a demonstration plant that will trial Direct Lithium Extraction (DLE) from the deep geothermal fluid. This paper presents an overview of the initial results of drilling and testing, briefly highlighting the success of hydraulic stimulation and management of induced seismicity during development. It also provides a forward look to the final stages of the United Downs development and the future of geothermal power projects across Cornwall. © 2022 Geothermal Resources Council. All rights reserved.